The first network is a network, for example, an ad hoc network for connection of communication units directly or through another communication unit by cable or by wireless without using a network connection device such as a router, an access point, a base station, etc.
Furthermore, the second network having a protocol different from the protocol of the first network is a network, for example, a LAN (local area network) for collecting various types of information from a node as a terminal configuring, for example, an ad hoc network. In the second network, communication units are connected through, for example, a network connection device.
As a configuration in which the first and second networks are connected, for example, a switch in a LAN is connected to a network relay node as a communication unit in an ad hoc network, and is connected to a server computer as a communication unit in a LAN (hereafter simply referred to as a “server”). Then, the server in the LAN controls each node in the ad hoc network or collects information from each node.
As an example of the configuration above, a server for collecting the sensor information in the LAN collects various types of sensor information from a node in an ad hoc network operating as sensor equipment.
With the above-mentioned configuration in which the first and second networks are connected, assume that broadcast information is transmitted from the server in the second network to the first network.
For example, in FIG. 1, the broadcast information transmitted from a server 1 in the LAN is received by a switch SW. After recognizing the broadcast information, the SW transmits the broadcast information to the node B in the connected ad hoc network. After receiving the broadcast information, the node B transmits the broadcast information to all ports connected to the local node, for example, to the node A and other nodes.
In this case, in the first network such as an ad hoc network etc., each node configuring the network has a mesh-shaped connection configuration. Therefore, a route is physically looped. When the communication information is looped, normal routing is not performed. However, a system in which the communication information passing through the route is not looped although the route is physically looped is incorporated into the first network.
In the communication system capable of communicating independent of the protocol of a network layer between an ad hoc network and a communication device on a LAN segment connected to the ad hoc network, there is a technique of determining a communication device as a destination of a frame from the path table to the communication device in the ad hoc network (for example, the patent document 1).    Patent Document 1: Japanese Laid-open Patent Publication No. 2006-279168